Method for transmitting signal for MTC and apparatus for same

ABSTRACT

A method is provided for performing a random access procedure by a user equipment (UE) in a wireless communication system supporting coverage enhancement. The UE repeatedly transmits a physical random access channel (PRACH) signal, determines a random access radio network temporary identifier (RA-RNTI) corresponding to the PRACH signal using system frame number (SFN) information, wherein time index information and frequency index information are not used for determining the RA-RNTI, and monitors downlink control information masked by the determined RA-RNTI. The time index information indicates a subframe starting the repeated transmission of the PRACH signal, the frequency index information indicates a frequency index of the PRACH signal transmitted in the starting subframe, and the SFN information indicates a radio frame starting the repeated transmission of the PRACH signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.14/903,528 filed on Jan. 7, 2016 (now U.S. Pat. No. 9,854,609 issued onDec. 26, 2017), which was filed as the National Phase of PCTInternational Application No. PCT/KR2014/006889 filed on Jul. 28, 2014,which claims priority under 35 U.S.C. 119(e) to U.S. ProvisionalApplication Nos. 61/939,291 filed on Feb. 13, 2014, 61/929,107 filed onJan. 19, 2014, 61/928,003 filed on Jan. 16, 2014, 61/925,664 filed Jan.10, 2014, 61/921,520 filed on Dec. 29, 2013, 61/919,825 filed on Dec.23, 2013, 61/910,970 filed on Dec. 3, 2013, 61/906,424 filed on Nov. 20,2013, 61/903,413 filed on Nov. 13, 2013, 61/897,200 filed on Oct. 29,2013, 61/894,904 filed on Oct. 23, 2013, 61/884,979 filed on Sep. 30,2013, 61/863,450 filed on Aug. 8, 2013, 61/862,526 filed on Aug. 6, 2013and 61/858,633 filed on Jul. 26, 2013, all of which are hereby expresslyincorporated by reference into the present application.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a method and apparatus for transmittinga signal in a wireless communication system. More particularly, thepresent invention relates to a method and apparatus for transmitting andreceiving a signal for machine type communication (MTC).

Background Art

Recently, wireless communication systems are widely developed to providevarious kinds of communication services including audio communications,data communications and the like. Generally, a wireless communicationsystem is a kind of a multiple access system capable of supportingcommunications with multiple users by sharing available system resources(e.g., bandwidth, transmission power, etc.). For instance, multipleaccess systems include CDMA (code division multiple access) system, FDMA(frequency division multiple access) system, TDMA (time divisionmultiple access) system, OFDMA (orthogonal frequency division multipleaccess) system, SC-FDMA (single carrier frequency division multipleaccess) system, MC-FDMA (multi carrier frequency division multipleaccess) and the like. In a wireless communication system, a userequipment (UE) may receive information from a base station in downlink(DL), and the user equipment may transmit information to the basestation in uplink (UL). The information transmitted or received by theUE may include data and various control information. In addition, thereare various physical channels according to the type or use of theinformation transmitted or received by the UE.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and apparatusfor effectively transmitting and receiving a signal in a wirelesscommunication system, and more specifically, to provide a method andapparatus for effectively transmitting and receiving a signal formachine type communication (MTC).

Another object of the present invention is to provide a method andapparatus for effective signal transmission and reception for coverageenhancement in a wireless communication system, and more specifically,to provide effective signal configuration and transceive timing when thesame signal is repeatedly transmitted and received for coverageenhancement in a wireless communication system.

Another object of the present invention is to provide a method andapparatus for effectively signaling/configuring information involved ina random access procedure in a wireless communication system, and morespecifically, to provide a method and apparatus for effectivelysignaling/configuring information involved in a random access procedurebased on repeated transmission for coverage enhancement in a wirelesscommunication system.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

In an aspect of the present invention, provided herein is a method forperforming a random access procedure by a user equipment (UE) in awireless communication system supporting repeated transmission of a samesignal, the method comprising: repeatedly transmitting a physical randomaccess channel (PRACH) signal using a PRACH resource; and receiving arandom access response signal in a specific time interval in response tothe PRACH signal, wherein the random access response signal comprisesinformation about a repeated transmission number of the PRACH signal.

Preferably, the method further comprises receiving system informationcomprising information about the PRACH resource and information aboutthe specific time interval, wherein the information about the specifictime interval is independently configured per information about thePRACH resource.

Preferably, the method further comprises receiving downlink controlinformation for scheduling the random access response signal, whereinthe downlink control information is masked with random access radionetwork temporary identifier (RA-RNTI) information and the RA-RNTIinformation is determined according to the repeated transmission numberof the PRACH signal.

Preferably, information about a repeated transmission subframe of thePRACH signal and information about a transmitting frequency of the PRACHsignal are not used to determine the RA-RNTI information.

In another aspect of the present invention, provided herein is a userequipment (UE) for transmitting and receiving a signal in a wirelesscommunication system supporting repeated transmission of a same signal,the UE comprising: a radio frequency (RF) unit; and a processoroperatively connected to the RF unit and configured to: repeatedlytransmit a physical random access channel (PRACH) signal using a PRACHresource, and receive a random access response signal in a specific timeinterval in response to the PRACH signal; and the random access responsesignal comprises information about a repeated transmission number of thePRACH signal.

Preferably, the processor is further configured to receive systeminformation comprising information about the PRACH resource andinformation about the specific time interval; and the information aboutthe specific time interval is independently configured per informationabout the PRACH resource.

Preferably, the processor is further configured to receive downlinkcontrol information for scheduling the random access response signal;and the downlink control information is masked with random access radionetwork temporary identifier (RA-RNTI) information and the RA-RNTIinformation is determined according to the repeated transmission numberof the PRACH signal.

Preferably, information about a repeated transmission subframe of thePRACH signal and information about a transmitting frequency of the PRACHsignal are not used to determine the RA-RNTI information.

Preferably, the system information further comprises information about arepetition number and a repetition configuration and start subframe forthe random access response signal, information about an orthogonalfrequency divisional multiplexing (OFDM) symbol in which transmission ofthe random access response signal is started, information about arepetition number and a repetition start and configuration subframe fora physical downlink control channel (PDCCH) signal for scheduling therandom access response signal, and information about a resource fortransmitting of the PDCCH signal.

Preferably, the system information further comprises information about arepetition number and a repetition start and configuration subframe foran uplink signal transmitted in response to the random access responsesignal, and information about a repetition number and a repetitioninterval for a physical hybrid automatic repeat request (HARQ) indicatorchannel (PHICH) signal corresponding to the uplink signal.

According to the present invention, a signal may be effectivelytransmitted and received in a wireless communication system, and morespecifically, a signal may be effectively transmitted and received in awireless communication system for machine type communication (MTC).

According to the present invention, a signal may be effectivelytransmitted and received for coverage enhancement in a wirelesscommunication system, and more specifically, a signal may be effectivelyconfigured and transceiving timing may be effectively determined whenthe same signal is repeatedly transmitted and received for coverageenhancement in a wireless communication system.

According to the present invention, information involved in a randomaccess procedure may be effectively signaled/configured in a wirelesscommunication system, and more specifically, information involved in arandom access procedure based on repeated transmission for coverageenhancement may be effectively signaled/configured in a wirelesscommunication system in a wireless communication system.

It will be appreciated by persons skilled in the art that that theeffects that could be achieved with the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 illustrates physical channels and a general method fortransmitting signals on the physical channels in the present invention.

FIG. 2 illustrates a structure of a radio frame used in the presentinvention.

FIG. 3 illustrates a resource grid of one DL slot used in the presentinvention.

FIG. 4 illustrates a downlink subframe structure used in the presentinvention.

FIG. 5 illustrates an example of allocating an E-PDCCH in a subframe.

FIG. 6 illustrates an exemplary structure of an uplink subframe that maybe used in LTE(-A) system.

FIG. 7 illustrates a random access procedure.

FIG. 8 illustrates a bundle interval according to the present invention.

FIGS. 9 and 10 illustrate exemplary methods according to the presentinvention.

FIG. 11 illustrates a BS and a UE to which the present invention isapplicable.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following embodiments of the present invention can be applied to avariety of wireless access technologies, for example, code divisionmultiple access (CDMA), frequency division multiple access (FDMA), timedivision multiple access (TDMA), orthogonal frequency division multipleaccess (OFDMA), single carrier frequency division multiple access(SC-FDMA), and the like. CDMA may be embodied through wireless (orradio) technology such as universal terrestrial radio access (UTRA) orCDMA2000. TDMA may be embodied through wireless (or radio) technologysuch as global system for mobile communication (GSM)/general packetradio service (GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMAmay be embodied through wireless (or radio) technology such as instituteof electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802-20, and evolved UTRA (E-UTRA). UTRA is a partof universal mobile telecommunications system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of E-UMTS(Evolved UMTS), which uses E-UTRA. LTE-Advanced (LTE-A) is an evolvedversion of 3GPP LTE.

For clarity of explanations, the following description focuses on 3GPPLTE(-A) system. However, technical principles of the present inventionare not limited thereto. Further, a particular terminology is providedfor better understanding of the present invention. However, such aparticular terminology may be changed without departing from thetechnical principles of the present invention. For example, the presentinvention may be applied to a system in accordance with a 3GPP LTE/LTE-Asystem as well as a system in accordance with another 3GPP standard,IEEE 802.xx standard, 3GPP2 standard, or a next-generation communicationstandard.

In a wireless access system, a user equipment (UE) may receiveinformation from a BS in downlink (DL) and transmit information inuplink (UL). The information transmitted or received by the UE mayinclude data and various control information. In addition, there arevarious physical channels according to the type or use of theinformation transmitted or received by the UE.

FIG. 1 illustrates physical channels and a general method fortransmitting signals on the physical channels in the present invention.

When a UE is powered on or enters a new cell, the UE performs initialcell search in step S101. The initial cell search involves acquisitionof synchronization to an eNB. To this end, the UE synchronizes itstiming to the eNB and acquires information such as a cell identifier(ID) by receiving a primary synchronization channel (P-SCH) and asecondary synchronization channel (S-SCH) from the eNB. Then the UE mayacquire broadcast information in the cell by receiving a physicalbroadcast channel (PBCH) from the eNB. During the initial cell search,the UE may monitor a DL channel state by receiving a downlink referencesignal (DL RS).

After the initial cell search, the UE may acquire more detailed systeminformation by receiving a physical downlink control channel (PDCCH) andreceiving a physical downlink shared channel (PDSCH) based oninformation of the PDCCH in step S102.

To complete access to the eNB, the UE may perform a random accessprocedure such as steps S103 to S106 with the eNB. To this end, the UEmay transmit a preamble on a physical random access channel (PRACH)(S103) and may receive a response message to the preamble on a PDCCH anda PDSCH associated with the PDCCH (S104). In the case of acontention-based random access, the UE may additionally perform acontention resolution procedure including transmission of an additionalPRACH (S105) and reception of a PDCCH signal and a PDSCH signalcorresponding to the PDCCH signal (S106).

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S107) and transmit a physical uplink shared channel(PUSCH) and/or a physical uplink control channel (PUCCH) to the eNB(S108), in a general UL/DL signal transmission procedure. Informationthat the UE transmits to the eNB is called Uplink Control Information(UCI). The UCI includes hybrid automatic repeat and requestacknowledgement/negative acknowledgement (HARQ-ACKNACK), schedulingrequest (SR), channel state information (CSI), etc. The CSI includeschannel quality indicator (CQI), precoding matrix indicator (PMI), rankindication (RI), etc. UCI is generally transmitted on a PUCCHperiodically. However, if control information and traffic data should betransmitted simultaneously, they may be transmitted on a PUSCH. Inaddition, the UCI may be transmitted aperiodically on the PUSCH, uponreceipt of a request/command from a network.

FIG. 2, including views (a) and (b), illustrates a structure of a radioframe used in the present invention. In a cellular OFDM radio packetcommunication system, uplink/downlink data packet transmission isperformed in subframe units and one subframe is defined as apredetermined duration including a plurality of OFDM symbols. TheLTE(-A) standard supports a type-1 radio frame structure applicable tofrequency division duplex (FDD) and a type-2 radio frame structureapplicable to time division duplex (TDD).

FIG. 2(a) shows the structure of the type-1 radio frame. A downlinkradio frame includes 10 subframes and one subframe includes two slots ina time domain. A time required to transmit one subframe is referred toas a transmission time interval (TTI). For example, one subframe has alength of 1 ms and one slot has a length of 0.5 ms. One slot includes aplurality of OFDM symbols in a time domain and includes a plurality ofresource blocks (RBs) in a frequency domain. In the LTE(-A) system,since OFDMA is used in downlink, an OFDM symbol indicates one symbolperiod. The OFDM symbol may be referred to as an SC-FDMA symbol orsymbol period. A RB as a resource assignment unit may include aplurality of consecutive subcarriers in one slot.

The number of OFDM symbols included in one slot may be changed accordingto the configuration of a cyclic prefix (CP). The CP includes anextended CP and a normal CP. For example, if OFDM symbols are configuredby the normal CP, the number of OFDM symbols included in one slot may be7. If OFDM symbols are configured by the extended CP, since the lengthof one OFDM symbol is increased, the number of OFDM symbols included inone slot is less than the number of OFDM symbols in case of the normalCP. In case of the extended CP, for example, the number of OFDM symbolsincluded in one slot may be 6. In the case where a channel state isunstable, such as the case where a UE moves at a high speed, theextended CP may be used in order to further reduce inter-symbolinterference.

FIG. 2(b) shows the structure of the type-2 radio frame. The type-2radio frame includes two half frames and each half frame includes fivesubframes, a downlink pilot time slot (DwPTS), a guard period (GP) andan uplink pilot time slot (UpPTS). One subframe includes two slots. Forexample, a downlink slot (e.g., DwPTS) is used for initial cell search,synchronization or channel estimation of a UE. For example, an uplinkslot (e.g., UpPTS) is used for channel estimation of a BS and uplinktransmission synchronization of a UE. For example, the uplink slot(e.g., UpPTS) may be used to transmit a sounding reference signal (SRS)for channel estimation in an eNB and to transmit a physical randomaccess channel (PRACH) that carriers a random access preamble for uplinktransmission synchronization. The GP is used to eliminate interferencegenerated in uplink due to multi-path delay of a downlink signal betweenuplink and downlink. Table 1 below shows an uplink (UL)-downlink (DL)configuration in subframes in a radio frame in a TDD mode.

TABLE 1 Downlink- to-Uplink Uplink- Switch- downlink point Subframenumber configuration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U DS U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  DS U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D DD D 6 5 ms D S U U U D S U U D

In Table 1 above, D represents a DL subframe, U represents a ULsubframe, and S represents a special subframe. The special subframeincludes a downlink pilot timeslot (DwPTS), a guard period (GP), and anuplink pilot timeslot (UpPTS). Table 2 below shows a special subframeconfiguration.

TABLE 2 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Normal Extended Normal Extended Special subframecyclic prefix cyclic prefix cyclic prefix cyclic prefix configurationDwPTS in uplink in uplink DwPTS in uplink in uplink 0  6592 · T_(s) 2192· T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592· T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

The above-described radio frame structure is purely exemplary and thusthe number of subframes in a radio frame, the number of slots in asubframe, or the number of symbols in a slot may vary in different ways.

FIG. 3 illustrates a resource grid of one DL slot used in the presentinvention.

Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols inthe time domain. One DL slot may include 7 OFDM symbols and a resourceblock (RB) may include 12 subcarriers in the frequency domain. However,the present invention is not limited thereto. Each element of theresource grid is referred to as a Resource Element (RE). An RB includes12×7 REs. The number of RBs in a DL slot, N^(DL) depends on a DLtransmission bandwidth. A UL slot may have the same structure as a DLslot.

FIG. 4 illustrates a downlink subframe structure used in the presentinvention.

Referring to FIG. 4, a maximum of three (or four) OFDM symbols locatedin a front portion of a first slot within a subframe correspond to acontrol region to which a control channel is allocated. The remainingOFDM symbols correspond to a data region to which a physical downlinkshared chancel (PDSCH) is allocated. A basic resource unit of the dataregion is RB. Examples of downlink control channels used in the LTE(-A)system include a physical control format indicator channel (PCFICH), aphysical downlink control channel (PDCCH), a physical hybrid ARQindicator channel (PHICH), etc.

PCFICH is transmitted at the first (or starting) OFDM symbol of asubframe and carries information regarding the number of OFDM symbolsused for transmission of control channels within the subframe. ThePCFICH is composed of four resource element groups (REGs) that areuniformly distributed in a control region based on a cell ID. One REGmay comprise 4 resource elements. The PCFICH indicates a value of 1 to 3(or 2 to 4) and is modulated via quadrature phase shift keying (QPSK).The PHICH is a response of uplink transmission and carries an HARQacknowledgment (ACK)/not-acknowledgment (NACK) signal. The PHICH exceptfor CRS and PCFICH (a first OFDM symbol) is allocated on the remainingREGs in one or more OFDM symbols configured by PHICH duration. The PHICHis allocated to three REGs that are distributed if possible on thefrequency domain. More detailed description regarding PHICH will beprovided below in the present specification.

The PDCCH is allocated in first n OFDM symbols (hereinafter, a controlregion) of a subframe. Here, n is an integer equal to or greater than 1and is indicated by the PCFICH. Control information transmitted throughthe PDCCH is referred to as downlink control information (DCI). A PDCCHmay carry a transport format and a resource allocation of a downlinkshared channel (DL-SCH), resource allocation information of an uplinkshared channel (UL-SCH), paging information on a paging channel (PCH),system information on the DL-SCH, information on resource allocation ofan upper-layer control message such as a random access responsetransmitted on the PDSCH, a set of Tx power control commands onindividual UEs within an arbitrary UE group, a Tx power control command,information on activation of a voice over IP (VoIP), etc. DCI formatoptionally includes information about hopping flag, RB allocation,modulation coding scheme (MCS), redundancy version (RV), new dataindicator (NDI), transmit power control (TPC), cyclic shift demodulationreference signal (DM-RS), channel quality information (CQI) request,HARQ process number, transmitted precoding matrix indicator (TPMI),precoding matrix indicator (PMI) confirmation, etc. according to itsusage.

A plurality of PDCCHs can be transmitted within a control region. The UEcan monitor the plurality of PDCCHs. The PDCCH is transmitted on anaggregation of one or several consecutive control channel elements(CCEs). The CCE is a logical allocation unit used to provide the PDCCHwith a coding rate based on a state of a radio channel. The CCEcorresponds to a plurality of resource element groups (REGs). A formatof the PDCCH and the number of bits of the available PDCCH aredetermined by the number of CCEs. The BS determines a PDCCH formataccording to DCI to be transmitted to the UE, and attaches a cyclicredundancy check (CRC) to control information. The CRC is masked with aunique identifier (referred to as a radio network temporary identifier(RNTI)) according to an owner or usage of the PDCCH. If the PDCCH is fora specific UE, a unique identifier (e.g., cell-RNTI (C-RNTI)) of the UEmay be masked to the CRC. Alternatively, if the PDCCH is for a pagingmessage, a paging identifier (e.g., paging-RNTI (P-RNTI)) may be maskedto the CRC. If the PDCCH is for system information (more specifically, asystem information block (SIB)), a system information RNTI (SI-RNTI) maybe masked to the CRC. When the PDCCH is for a random access response, arandom access-RNTI (RA-RNTI) may be masked to the CRC. When the PDCCH isfor uplink power control, transmit power control-RNTI (TPC-RNTI) may beused, and the TPC-RNTI may include TPC-PUCCH-RNTI for PUCCH powercontrol and TPC-PUSCH-RNTI for PUSCH power control. When the PDCCH isfor multicast control channel (MCCH), multimedia broadcast multicastservice-RNTI (M-RNTI) may be used.

Each PDCCH is transmitted using one or more control channel elements(CCEs) and each CCE corresponds to nine sets of four resource elements.The four resource elements are referred to as a resource element group(REG). Four QPSK symbols are mapped to one REG. A resource elementallocated to a reference signal is not included in an REG and thus atotal number of REGs in a given OFDM symbol varies according to whethera cell-specific reference signal is present.

Table 3 shows the number of CCEs, the number of REGs, and the number ofPDCCH bits according to PDCCH format.

TABLE 3 Number of PDCCH format Number of CCE (n) Number of REG PDCCHbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

CCEs are sequentially numbered. To simplify a decoding process,transmission of a PDCCH having a format including n CCEs can be startedusing as many CCEs as a multiple of n. The number of CCEs used totransmit a specific PDCCH is determined by a BS according to channelcondition. For example, if a PDCCH is for a UE having a high-qualitydownlink channel (e.g., a channel close to the BS), only one CCE can beused for PDCCH transmission. However, for a UE having a poor channel(e.g., a channel close to a cell edge), 8 CCEs can be used for PDCCHtransmission in order to obtain sufficient robustness. In addition, apower level of the PDCCH can be controlled according to channelcondition.

Control information transmitted through the PDCCH is referred to asdownlink control information (DCI). Various DCI formats are definedaccording to their usage. Specifically, DCI format 0, 4 (hereinafter, ULgrant) are defined for uplink scheduling, and DCI formats 1, 1A, 1B, 1C,1D, 2, 2A, 2B, 2C, and 2D (hereinafter, DL grant) are defined fordownlink scheduling. DCI format optionally includes information abouthopping flag, RB allocation, modulation coding scheme (MCS), redundancyversion (RV), new data indicator (NDI), transmit power control (TPC),cyclic shift demodulation reference signal (DM-RS), channel qualityinformation (CQI) request, HARQ process number, transmitted precodingmatrix indicator (TPMI), precoding matrix indicator (PMI) confirmation,etc. according to its usage.

A base station determines a PDCCH format according to controlinformation to be transmitted to a UE, and attaches a cyclic redundancycheck (CRC) to the control information for error detection. CRC ismasked with an identifier (e.g., radio network temporary identifier(RNTI)) according to an owner or usage of the PDCCH. In other words,PDCCH is CRC-scrambled with an identifier (e.g., RNTI).

The LTE(-A) system defines a limited set of CCE positions in which aPDCCH is to be positioned for each UE. A limited set of CCE positionsthat a UE can find a PDCCH of the UE may be referred to as a searchspace (SS). In the LTE(-A) system, the SS has different sizes accordingto each PDCCH format. In addition, a UE-specific SS and a common SS areseparately defined. The BS does not provide the UE with informationindicating where the PDCCH is located in the control region.Accordingly, the UE monitors a set of PDCCH candidates within thesubframe and finds its own PDCCH. The term “monitoring” means that theUE attempts to decode the received PDCCHs according to respective DCIformats. The monitoring for a PDCCH in an SS is referred to as blinddecoding (blind detection). Through blind decoding, the UEsimultaneously performs identification of the PDCCH transmitted to theUE and decoding of the control information transmitted through thecorresponding PDCCH. For example, in the case where the PDCCH isde-masked using the C-RNTI, the UE detects its own PDCCH if a CRC erroris not detected. The USS is separately configured for each UE and ascope of CSSs is known to all UEs. The USS and the CSS may be overlappedwith each other. When a significantly small SS is present, if some CCEpositions are allocated in an SS for a specific UE, the remaining CCEsare not present. Thus a BS may not find CCE resources in which the PDCCHis to be transmitted to all available UEs in a given subframe. In orderto minimize the possibility that such blocking is subsequent to a nextsubframe, a start position of the USS is UE-specifically hopped.

Table 4 shows sizes of CSS and USS.

TABLE 4 Number Number of Number of PDCCH format of CCE (n) candidates inCSS candidates in USS 0 1 — 6 1 2 — 6 2 4 4 2 3 8 2 2

To control computational load of blind decoding based on the number ofblind decoding processes to an appropriate level, the UE is not requiredto simultaneously search for all defined DCI formats. In general, the UEsearches for formats 0 and 1A at all times in the UE-specific searchspace. Formats 0 and 1A have the same size and are discriminated fromeach other by a flag in a message. The UE may need to receive anadditional format (e.g., format 1, 1B or 2 according to PDSCHtransmission mode set by a BS). The UE searches for formats 1A and 1C inthe UE-common search space. Furthermore, the UE may be set to search forformat 3 or 3A. Formats 3 and 3A have the same size as that of formats 0and 1A and may be discriminated from each other by scrambling CRC withdifferent (common) identifiers rather than a UE-specific identifier.

A PDSCH transmission scheme and information contents of DCI formatsaccording to a transmission mode will be listed below.

Transmission Mode (TM)

-   -   Transmission Mode 1: Transmission from a single eNB antenna port    -   Transmission Mode 2: Transmit diversity    -   Transmission Mode 3: Open-loop spatial multiplexing    -   Transmission Mode 4: Closed-loop spatial multiplexing    -   Transmission Mode 5: Multi-user MIMO    -   Transmission Mode 6: Closed-loop rank-1 precoding    -   Transmission Mode 7: Single-antenna port (port 5) transmission    -   Transmission Mode 8: Dual layer transmission (ports 7 and 8) or        single-antenna port (port 7 or 8) transmission    -   Transmission Modes 9 and 10: Layer transmission up to rank 8        (ports 7 to 14) or single-antenna port (port 7 or 8)        transmission

DCI Format

-   -   Format 0: Resource grant for PUSCH transmission    -   Format 1: Resource allocation for single codeword PUSCH        transmission (transmission modes 1, 2, and 7)    -   Format 1A: Compact signaling of resource allocation for single        codeword PDSCH transmission (all modes)    -   Format 1B: Compact resource allocation for PDSCH (mode 6) using        rank-1 closed-loop precoding    -   Format 1C: Very compact resource allocation for PDSCH (e.g.,        paging/broadcast system information)    -   Format 1D: Compact resource allocation for PDSCH (mode 5) using        multi-user MIMO    -   Format 2: Resource allocation for PDSCH (mode 4) of closed-loop        MIMO operation    -   Format 2A: Resource allocation for PDSCH (mode 3) of open-loop        MIMO operation    -   Format 3/3A: Power control command with 2-bit/1-bit power        adjustments for PUCCH and PUSCH    -   Format 4: Resource grant for PUSCH transmission (uplink) in a        cell configured in a multi-antenna port transmission mode

DCI formats may be classified as a TM-dedicated format and TM-commonformat. The TM-dedicated format indicates a DCI format configured onlyfor the corresponding TM, and the TM-common format indicates a DCIformat configured commonly for all TMs. For example, DCI format 2B maybe a TM-dedicated DCI format for TM 8, DCI format 2C may be aTM-dedicated DCI format for TM 9, DCI format 2D may be a TM-dedicatedDCI format for TM 10. Further, DCI format 1A may be a TM-common DCIformat.

FIG. 5 illustrates an example of allocating an E-PDCCH in a subframe. Inthe conventional LTE system, PDCCH has a limitation of being transmittedin a limited number of symbols. Thus, in the LTE-A system, enhancedPDCCH (E-PDCCH) has been introduced for more flexible scheduling.

Referring to FIG. 5, a PDCCH (for convenience, legacy PDCCH or L-PDCCH)used in the conventional LTE(-A) system may be allocated to a controlregion of a subframe. An L-PDCCH region refers to a region to which thelegacy PDCCH can be allocated. In the context, the L-PDCCH region may bereferred to as a control region, a control channel resource region(i.e., a CCE resource) to which a PDCCH can be actually allocated, or aPDCCH search space. A PDCCH may be additionally allocated in a dataregion (e.g., a resource region for a PDSCH, refer to FIG. 4). The PDCCHallocated to the data region is referred to as an E-PDCCH. Asillustrated, a channel resource may be additionally ensured through theE-PDCCH to alleviate scheduling restrictions due to limited controlchannel resource of an L-PDCCH region. The E-PDCCH and a PDSCH aremultiplexed in a data region in the manner of frequency divisionmultiplexing (FDM).

In detail, the E-PDCCH may be detected/demodulated based on a DM-RS. TheE-PDCCH may be configured to be transmitted over a PRB pair on a timeaxis. When E-PDCCH based scheduling is configured, a subframe fortransmission/detection of an E-PDCCH may be designated. The E-PDCCH maybe configured in only a USS. The UE may attempt DCI detection only on anL-PDCCH CSS and an E-PDCCH USS in a subframe (hereinafter, an E-PDCCHsubframe) in which E-PDCCH transmission/detection is configured and mayattempt DCI detection on an L-PDCCH CSS and an L-PDCCH USS in a subframe(non-E-PDCCH subframe) in which transmission/detection of E-PDCCH is notallowed.

Like an L-PDCCH, an E-PDCCH carries DCI. For example, the E-PDCCH maycarry DL scheduling information and UL scheduling information. AnE-PDCCH/PDSCH procedure and an E-PDCCH/PUSCH procedure are thesame/similar as described in steps S107 and S108 of FIG. 1. That is, aUE may receive the E-PDCCH and receive data/control information througha PDSCH corresponding to the E-PDCCH. In addition, the UE may receivethe E-PDCCH and transmit data/control information through a PUSCHcorresponding to the E-PDCCH. The conventional LTE system pre-reserves aPDCCH candidate region (hereinafter, a PDCCH search space) in a controlregion and transmits a PDCCH of a specific UE in a part of the PDCCHcandidate region. Accordingly, the UE may acquire a PDCCH of the UE inthe PDCCH search space via blind decoding. Similarly, the E-PDCCH may betransmitted over a part or entire portion of a pre-reserved resource.

FIG. 6 illustrates an exemplary structure of an uplink subframe that maybe used in LTE(-A) system.

Referring to FIG. 6, the uplink subframe includes a plurality of slots(for example, two). Each slot may include a plurality of SC-FDMAsymbols, wherein the number of SC-FDMA symbols included in each slot isvaried depending on a cyclic prefix (CP) length. In an example, a slotmay comprise 7 SC-FDMA symbols in case of normal CP. An uplink subframeis divided into a data region and a control region in a frequencydomain. The data region includes a PUSCH, and is used to transmit a datasignal that includes voice information. The control region includes aPUCCH, and is used to transmit uplink control information (UCI). ThePUCCH includes RB pair (e.g., m=0, 1, 2, 3) located at both ends of thedata region on a frequency axis, and performs hopping on the border ofthe slots.

The PUCCH may be used to transmit the following control information.

-   -   SR (Scheduling Request): information used to request uplink        UL-SCH resource. The SR is transmitted using an on-off keying        (00K) scheme.    -   HARQ ACK/NACK: a response signal to the PDCCH indicating        semi-persistent scheduling (SPS) release and a downlink data        packet on the PDSCH. HARQ ACK/NACK represents whether the PDCCH        indicating SPS release or the downlink data packet has been        successfully received. ACK/NACK 1 bit is transmitted in response        to a single downlink codeword (CW), and ACK/NACK 2 bits are        transmitted in response to two downlink codewords.    -   CQI (Channel Quality Indicator): feedback information on a        downlink channel. MIMO (Multiple Input Multiple Output) related        feedback information includes a rank indicator (RI) and a        precoding matrix indicator (PMI). 20 bits per subframe are used.

FIG. 7 illustrates a random access procedure.

The random access procedure is used to transmit short-length data inuplink. For example, the random access procedure is performed uponinitial access in an RRC_IDLE mode, upon initial access after radio linkfailure, upon handover requiring the random access procedure, and uponthe occurrence of uplink/downlink data requiring the random accessprocedure during an RRC_CONNECTED mode. Some RRC messages such as an RRCconnection request message, a cell update message, and a URA updatemessage are transmitted using a random access procedure. Logicalchannels such as a Common Control Channel (CCCH), a Dedicated ControlChannel (DCCH), or a Dedicated Traffic Channel (DTCH) can be mapped to atransport channel (RACH). The transport channel (RACH) can be mapped toa physical channel (e.g., Physical Random Access Channel (PRACH)). Whena UE MAC layer instructs a UE physical layer to transmit a PRACH, the UEphysical layer first selects an access slot and a signature andtransmits a PRACH preamble in uplink. The random access procedure isdivided into a contention-based procedure and a non-contention-basedprocedure.

With reference to FIG. 7, a UE receives and stores information regardingrandom access from an eNB through system information. Thereafter, whenrandom access is needed, the UE transmits a random access preamble(referred to as Message 1) to the eNB (S710). Upon receiving the randomaccess preamble from the UE, the eNB transmits a random access responsemessage (referred to as Message 2) to the UE (S720). Specifically,downlink scheduling information for the random access response messagemay be CRC-masked with a Random Access-RNTI and may be transmittedthrough an L1/L2 control channel (PDCCH). Upon receiving the downlinkscheduling signal masked with the RA-RNTI, the UE may receive and decodea random access response message from a Physical Downlink Shared Channel(PDSCH). Thereafter, the UE checks whether or not random access responseinformation corresponding to the UE is present in the received randomaccess response message. Whether or not random access responseinformation corresponding to the UE is present can be determined basedon whether or not a Random Access preamble ID (RAID) for the preamblethat the UE has transmitted is present. The random access responseinformation includes Timing Advance (TA) indicating timing offsetinformation for synchronization, information of allocation of radioresources used in uplink, and a temporary identity (e.g., T-CRNTI) foruser identification. Upon receiving the random access responseinformation, the UE transmits an uplink message (referred to as Message3) through an uplink Shared Channel (SCH) according to radio resourceallocation information included in the response information (S730).After receiving the uplink message from the UE, the eNB transmits amessage for contention resolution (referred to as Message 4) to the UE(S740).

In case of a non-contention based procedure, a base station may allocatea non-contention random access preamble to a UE before the UE transmitsa random access preamble (S710). The non-contention random accesspreamble may be allocated through a dedicated signaling such as ahandover command or PDCCH. In case that a UE is allocated with anon-contention random access preamble, the UE may transmit the allocatednon-contention random access preamble to a base station in a similarmanner as S710. If the base station receives the non-contention randomaccess preamble from the UE, the base station may transmit a randomaccess response (referred to as Message 2) to the UE in a similar manneras S720.

During the above-described random access procedure, HARQ may not beapplied to a random access response (S720), but HARQ may be applied toan uplink transmission for the random access response or a message forcontention resolution. Thus, the UE does not have to transmit ACK/NACKin response the random access response.

A next generation of LTE-A system is considering to configure a UE at alow cost/low specification mainly focusing on data communication such asmetering of a gauge meter, measurement of a water level, utilization ofa monitoring camera, inventory report of a vending machine, and thelike. Such a UE is referred to as a machine type communication (MTC) UEor low complexity type UE for convenience. The MTC UE has a low datatransmission amount and frequently transmits and receives data inuplink/downlink, and thus it is effective to reduce a cost of the deviceand battery consumption according to the low data transmission amount.The MTC UE has low mobility and thus a channel environment is rarelychanged. In consideration of a poor situation in which the MTC UE isinstalled in a coverage-limited place such as a basement as well as abuilding and a factory, research has currently been conducted intovarious coverage enhancement schemes such as a repeated transmissionmethod for a MTC UE for each channel/signal.

In the present specification, a UE according to a legacy LTE-A systemmay be referred to as a normal UE or a first type UE, and an MTC UE maybe referred to as a second type UE or low complexity type (LCT) UE.Alternatively, a UE with a normal coverage (to which repetition is notapplied) may be referred to as a first type UE, and a coverage-limitedUE (to which repetition is applied) may be referred to as a second UE oran LCT UE. Alternatively, a UE to which repetition of the samesignal/channel is not applied may be referred to as a first type UE, anda UE to which repetition is applied may be referred to as a second typeUE or a coverage enhanced (CE) UE. For example, in the case of thesecond type UE, the number of reception antennas may be reduced, thenumber of transport blocks (TBs) to be supported may be reduced, and atransmission and reception frequency range may be reduced. Morespecifically, the second type UE may have one transmit antenna and onereceive antenna, support only one TB, and support only a frequency rangeequal to or less than 6 resource blocks (RBs).

When a signal is transmitted in a coverage-limited environment, signalintensity may be weak as compared with noise. However, when the samesignal/channel is repeatedly transmitted, the signal intensity may becontinuously accumulated and may be increased, but noise has randomproperties and thus noise may be counter-balanced so as to be maintainedat a predetermined level. Accordingly, coverage may be enhanced viarepeated transmission of the same signal in a coverage-limitedenvironment.

In consideration of coverage enhancement in a random access procedure,(time domain) repetition may also be applied to a PRACH preambletransmission and a signal/channel transmitted in association with thePRACH preamble transmission, i.e., for example, a random access response(RAR), PUSCH (or Msg3) scheduled from the RAR, and the like.Accordingly, for repeated transmitting operation, a number of times ofapplying/performing repetition need to be signaled/configured using apredetermined resource (e.g., code/time/frequency) for eachsignal/channel prior to corresponding signal/channel transmission. Inaddition, in consideration of application of repetition to a PRACHpreamble and/or RAR and/or a PDCCH for scheduling the corresponding RAR,it is necessary to consider a method for determining a RA-RNTI and aninterval at which RAR can be received (and/or RA-RNTI can be detected).In this specification, the interval at which RAR can be received (and/orRA-RNTI can be detected) will be referred to as an RAR window.

The present invention proposes a method for signaling/configuringinformation and a parameter involved in a random access procedure basedon repeated transmission for coverage enhancement of a second type UE.In this specification, a PRACH resource may refer to a combination of asequence/subframe (SF)/frequency band, etc. used in PRACH preambletransmission. In addition, in the specification, a signal/channelrepeated transmission duration corresponding to one repetition number oftimes for repeated transmission of the same signal may be referred to as“bundle” or “bundle interval” for convenience. A repetition number oftimes for each signal/channel may be independently configured forcoverage enhancement, and the repetition number of times may include“1”. When a repetition number of times is 1, this means one-timetransmission without repetition and in this case, a bundle interval maybe one subframe. In addition, the PDCCH described in the presentinvention may include both a PDCCH and an EPDCCH, and the CCE mayinclude both a CCE and an ECCE. In the specification, the repeatedtransmission may be simply referred to as repetition. Prior to thedescription, several terms associated with a random access procedurewill be summarized below.

1) PRACH: PRACH preamble transmitted using a combination of a specificsequence/SF/frequency band (UE to eNB)

A. A repetition number of times of PRACH is defined as Np forconvenience.

B. In the case of PRACH repetition, a method for applying a repetitionnumber of times Np to an entire preamble format or applying a repetitionnumber of times Np only to a part of sequence within a preamble may beconsidered.

2) RAR: PDSCH for transmitting a PRACH preamble response messageincluding timing advance (TA), etc. (eNB to UE)

RAR-PDCCH: PDCCH for transmitting DL grant for RAR (eNB to UE)

A. A repetition number of times of RAR and RAR-PDCCH are defined as Nrand Nd, respectively.

3) Msg3: PUSCH transmitted based on UL grant included in RAR (UE to eNB)

A. A repetition number of times of Msg3 is defined as Nm

FIG. 8 illustrates a bundle interval according to the present invention.

Referring to FIG. 8, the same channel/signal may be transmitted andreceived once in one subframe and transmitted and received with aspecific offset a total of N repetition numbers over N (>0) subframes.In this case, a subframe in which a channel/signal is initiallytransmitted and received may be referred to as a bundle start subframe S(refer to FIG. 8), a subframe in which a channel/signal is lastlytransmitted and received may be referred to as a bundle end subframe,and an interval to the bundle end subframe from the bundle startsubframe may be referred to as a bundle or a bundle interval. Inaddition, a subframe in which a channel/signal is transmitted andreceived in a bundle or a bundle interval may be referred to as a bundleconfiguration subframe. Accordingly, the same channel/signal may betransmitted and received every bundle configuration subframe from thebundle start subframe S (refer to FIG. 8). In addition, subframesconstituting the bundle interval may each be configured with a specificoffset k. For example, when the specific offset k is 1, the bundleinterval may be configured with N consecutive subframes. In the presentspecification, for convenience of description, it may be assumed thatthe bundle interval includes consecutive subframes, but the presentinvention may also be applied to the case, in which an offset has avalue equal to or greater than 1, in the same manner.

RAR Transmission Related Information

In general, RAR transmission may be scheduled by an RAR-PDCCH (e.g.,refer to FIG. 7). Accordingly, in a general case, the RAR transmissionrelated information (briefly referred to as RAR-info) may include all orpart of the following information items. Below, an RAR-PDCCH repetitionnumber of times Nd, RAR-PDCCH bundle configuration/start SF information,control channel resource information for transmitting an RAR-PDCCH,and/or CFI information may be referred to as RAR-PDCCH transmissionrelated information.

-   -   RAR repetition number of times Nr    -   RAR bundle configuration/start SF information    -   Information on OFDM symbol in which RAR transmission is started    -   RAR-PDCCH repetition number of times Nd    -   RAR-PDCCH bundle configuration/start SF information    -   Information on a control channel resource (e.g., PDCCH candidate        and/or CCE index) for transmitting RAR-PDCCH and control format        indicator (CFI) information (i.e., OFDM symbol number/interval        used/assumed for transmitting a control channel of a PDCCH,        etc.)

RAR transmission related information (RAR-info) may besignaled/configured via (specific) SIB. The corresponding (specific) SIBmay be a legacy SIB that can also be received by normal UEs or a newsecond-type-dedicated SIB that can be received by all or only specificsecond type UEs. The legacy SIB may refer to SIB specified in the LTE-A,and when RAR transmission related information is signaled via the legacySIB, the RAR transmission related information may be signaled to beadditionally included in the legacy SIB. When the RAR transmissionrelated information is signaled via the second-type-dedicated SIB, theRAR transmission related information may be included in, for example,SIB that can be received by only second type UEs that require coverageenhancement.

In addition, RAR transmission related information may be defined forrespective coverage enhancement requirements in the form of a look-uptable. In this case, the second type UE may perform an RAR transmissionrelated operation based on the look-up table with reference toinformation corresponding to a coverage condition of the second type UEin the look-up table without an additional separatesignaling/configuring procedure.

In addition, repetition related information about an arbitrary PDCCHtransmitted through a common search space (CSS) (or based on UE-commonRNTI) may be signaled/configured via (specific) SIB (or RAR orUE-specific RRC signaling) with included in RAR-info or irrespective ofRAR-info. Repetition related information about an arbitrary PDCCHtransmitted via a common search space (CSS) (or based on UE-common RNTI)may be signaled/configured with including RAR-PDCCH repetition relatedinformation or irrespective of RAR-PDCCH repetition related information.The UE-common RNTI may include, for example, SI-RNTI, P-RNTI, RA-RNTI,TPC-PUCCH-RNTI, TPC-PUSCH-RNTI, or M-RNTI. Repetition relatedinformation about CSS (or UE-common RNTI) based PDCCH may refer to, forexample, all or part of PDCCH repetition number of times and PDCCHbundle configuration/start SF information, control channel resourceinformation for transmitting PDCCH, CFI information, etc.

In addition, the CSS (or UE-common RNTI) based PDCCH repetition relatedinformation may include PDSCH/PUSCH repetition related informationscheduled from the CSS (or UE-common RNTI) based PDCCH. For example,PDSCH/PUSCH repetition related information scheduled from the CSS (orUE-common RNTI) based PDCCH may include all or part of PDSCH/PUSCHrepetition number of times and PDSCH/PUSCH bundle configuration/start SFinformation, PDSCH transmission start OFDM symbol information, whetherPHICH transmission is present, PHICH repetition related information,whether HARQ-ACK is transmitted, HARQ-ACK repetition relatedinformation, etc. In addition, for example, the PHICH repetition relatedinformation may include all or part of PHICH repetition number of timesand PHICH bundle configuration/start SF information, PHICH resourceallocation information corresponding thereto, and the like. For example,the HARQ-ACK repetition related information may include all or part ofHARQ-ACK repetition number of times and HARQ-ACK bundleconfiguration/start SF information, resource allocation informationcorresponding thereto, and the like.

CSS (or UE-common RNTI) based PDCCH repetition related information (andPDSCH/PUSCH repetition related information corresponding thereto) may beindependently configured for each DCI format type/use and/or DCI payloadsize. For example, independent repetition related information may beconfigured from DCI format 0/1A and DCI format 3/3A and DCI format 1Caccording to a DCI format type/use or independent repetition relatedinformation may be configured for DCI format 0/1A/3/3A and DCI format 1Caccording to a DCI payload size. In addition, CSS (or UE-common RNTI)based PDCCH repetition related information (and PDSCH/PUSCH repetitionrelated information corresponding thereto) may be independentlyconfigured for each RNTI type and/or use. For example, independentrepetition related information may be configured for UE-common RNTI andUE-specific RNTI, or independent repetition related information may beconfigured for UE-specific RNTI and TPC-PUCCH/PUSCH-RNTI andRA/SI/P-RNTI (or RA-RNTI and SI/P-RNTI).

As another method, in order to reduce overhead and latency involved incontrol signaling, a method for (applying repetition and) transmittingonly RAR without RAR-PDCCH transmission may be considered. In this case,(except for RAR-PDCCH repetition related information) (all or part of)RAR repetition number of times Nr and RAR bundle configuration/start SFinformation, information about an OFDM symbol in which RAR transmissionis started, RAR scheduling information (e.g., MCS level and/or TB size),and the like as well as RB resources allocated to RAR transmission maybe included in RAR-info and may be signaled/configured via (specific)SIB.

On the other hand, a method for (applying repetition and) transmittingonly RAR-PDCCH without transmission of RAR (PDSCH including the same)may also be considered. In this case, the UE may operate whileconsidering the corresponding RAR-PDCCH as RAR. In this case, (exceptfor RAR transmission related information) (all or part of) RAR-PDCCHrepetition number of times Nd and RAR-PDCCH bundle configuration/startSF information, information about a control channel resource fortransmitting RAR-PDCCH, CFI information, and the like may be included inRAR-info and may be signaled/configured via (specific) SIB. In thiscase, all or part of RAR related content (e.g., timing advance (TA),temporary-C-RNTI, and UL grant for Msg3) may be included in a specificfield (combination) constituting RAR-PDCCH. Alternatively, UL grant(and/or temporary-C-RNTI) for Msg3 may be may be preconfigured via(specific) SIB.

According to an embodiment of the present invention, a PRACH resource ora PRACH resource set may be allocated to correspond to differentcoverage enhancement requirements and corresponding RAR transmissionrelated information (RAR-info) may be differently (or independently)configured for each PRACH resource or PRACH resource set. For example,coverage enhancement requirements may be defined as measured path-lossand/or required signal-to-noise ratio (SNR)/signal-to-interference plusnoise ratio (SINR). A UE may select/transmit a specific PRACH resourceaccording to a coverage condition (e.g., a measured path-loss value orcoverage enhancement requirements calculated based thereon (e.g., SNR orSINR)) of the UE and then perform an RAR detection/reception operationappropriate for RAR transmission related information (RAR-info)set/associated with a corresponding specific PRACH resource.

The PDSCH and/or PDCCH transmission related information may also besignaled/configured in the same/similar way (e.g., for each PRACHresource (set) and/or coverage enhancement requirements). The PDSCHand/or PDCCH transmission related information may be signaled/configuredby generalizing RAR transmission related information (RAR-info) orirrespective of RAR transmission related information (RAR-info). Forexample, the PDSCH and/or PDCCH transmission related information mayinclude all or part of PDSCH repetition number of times and PDSCH bundleconfiguration/start SF information, PDSCH start OFDM symbol information,PDCCH repetition number of times and PDCCH bundle configuration/start SFinformation, PDCCH transmission control channel resource and CFIinformation (including information on whether PCFICH reception isperformed or skipped), PDSCH scheduling information (e.g., MCS leveland/or TB size) (when a PDSCH is repeatedly transmitted withoutcorresponding PDCCH transmission), information about whether HARQ-ACKfor PDSCH reception is transmitted and/or HARQ-ACK repetition number oftimes/bundle information. In addition, for example, the UE may perform aPDSCH/PDCCH receiving operation appropriate for the PDSCH/PDCCHtransmission related information corresponding to a coverage conditionof the UE based on the PDSCH/PDCCH transmission related information.

During a detection/receiving operation of a primary synchronizationsignal (PSS)/secondary synchronization signal (SSS) and/or physicalbroadcast channel (PBCH), when the UE determines that there is a problemin coverage (e.g., measured path-loss and required S(I)NR) of the UE,CFI information to be assumed (e.g., for PDCCH detection/reception,etc.) by the UE needs to be pre-defined until the UE receives signalingfor actual CFI information configuration from an eNB. The case in whichthe UE determines that there is a problem in coverage of the UE mayinclude, for example, the case in which combining/acquisition time ofreception for PSS/SSS detection is relatively increased compared with ageneral legacy UE and/or the case in which a master information block(MIB) can be detected by only receiving a PBCH bundle including anadditional repeated PBCH as well as a legacy PBCH.

Accordingly, the present invention proposes that a UE (skips adetection/reception operation and) operates while assuming/consideringone specific CFI value irrespective of a system bandwidth (BW) or agreatest CFI value defined in a BW of a system that the UE accessesuntil receiving signaling for actual CFI information configuration fromthe eNB in a coverage-limited situation. For example, the UE may operatewhile assuming/considering a (as small as possible) PDSCH start OFDMsymbol index when the corresponding CFI values is assumed. In addition,the UE may operate while assuming/considering that PDSCH mapping startsfrom a symbol that immediately succeeds a control channel symbolduration corresponding to the greatest CFI value or a specific CFI valueuntil receiving signaling for actual PDSCH start OFDM symbol informationconfiguration from the eNB. In addition, the UE may skip a HARQ-ACKtransmitting operation for PDSCH reception until receiving signaling foractual HARQ-ACK feedback related information configuration from the eNB.

As another method, the UE may operate while assuming/considering agreatest CFI value (according to a system bandwidth (BW)) or a specificCFI value (irrespective of a system bandwidth (BW)) with respect to aPDSCH (referred to as “UE-common PDSCH”) for transmitting UE-common dataand operate while assuming/considering a different CFI value from theCFI value corresponding to the UE-common PDSCH with respect to PDSCH(referred to as “UE-specific PDSCH”) for transmitting UE-specific dataor signal/set separate independent CFI information (and/or PDSCH startsymbol information) with respect to only the corresponding UE-specificPDSCH. The UE-common PDSCH may include, for example, SIB and/or pagingand/or RAR, etc. For example, the UE may operate whileassuming/considering a (as small as possible) PDSCH start OFDM symbolindex when the corresponding CFI value is assumed.

The CFI information (and/or PDSCH start symbol information) may besignaled/configured via a PBCH, SIB, RAR, or Msg4 or may be UE-commonlysignaled/configured through a separate specific broadcast signal/channel(transmitted with a predetermined duration).

Msg3 Transmission Related Information

The Msg3 transmission related information may include all or part of thefollowing information items. The Msg3 transmission related informationmay be referred to as Msg3-info.

-   -   Msg3 repetition number of times Nm    -   Msg3 bundle configuration/start SF information    -   Whether a PHICH is transmitted in response to Msg3 reception.        When PHICH transmission is configured to be skipped, PHICH based        non-adaptive automatic retransmission may not be permitted and        only UL grant-based adaptive retransmission (adaptive        retransmission may be permitted.    -   PHICH repetition number of times/bundle information

The Msg3 transmission related information (Msg3-info) may besignaled/configured via (specific) SIB or RAR. Alternatively, as in thecase of RAR transmission related information (RAR-info), the aboveinformation items may be defined in the form of a look-up table for eachcoverage enhancement requirement. In this case, a second type UE mayperform a Msg3 transmission related operation based on informationappropriate for a coverage condition of the UE with reference to theinformation in the look-up table without a separate additionalsignaling/configuring procedure.

Start SF timing of Msg3 bundle transmission may be determined based onstart or end SF timing of RAR (or PDCCH corresponding thereto) bundletransmission. For example, the start SF timing of Msg3 bundletransmission may be determined as SF timing obtained by adding aspecific SF offset to the start or end SF timing of the RAR (or PDCCHcorresponding thereto) bundle transmission. The specific SF offset maybe, for example, signaled/set while included in the Msg3 transmissionrelated information (Msg3-info) or may be pre-defined as a specificvalue.

In addition, for transmission UL grant for scheduling retransmission ofMsg3 and/or DL grant for scheduling a specific PDSCH (referred to as“Msg4”) transmitted for contention resolution for Msg3, a PDCCH may berepeatedly transmitted through a specific UE-search space (USS) (orbased on UE-specific RNTI). The UE-specific RNTI may include, forexample, temporary C-RNTI, C-RNTI, and SPS C-RNTI. Repetition relatedinformation about a USS (or UE-specific RNTI) based PDCCH may besignaled/set via (specific) SIB or RAR (or UE-specific RRC signaling)while included in the Msg3 transmission related information (Msg3-info)or irrespective of Msg3 transmission related information (Msg3-info).Alternatively, the repetition related information about the USS (orUE-specific RNTI) based PDCCH may be independently signaled/configuredCSS (or UE-common RNTI) based PDCCH repetition related information (andPDSCH/PUSCH repetition related information corresponding thereto). Therepetition related information for the USS (or UE-specific RNTI) basedPDCCH may refer to all or part of PDCCH repetition number of times andPDCCH bundle configuration/start SF information, information of controlchannel resource for transmitting a PDCCH, CFI information, etc.

In addition, the USS (or UE-specific RNTI) based PDCCH repetitionrelated information may include PDSCH/PUSCH repetition relatedinformation scheduled from a USS (or UE-specific RNTI) based PDCCH. Forexample, the PDSCH/PUSCH repetition related information may include allor part of PDSCH/PUSCH repetition number of times and PDSCH/PUSCH bundleconfiguration/start SF information, PDSCH transmission start OFDM symbolinformation, information about whether a PHICH is transmitted and PHICHrepetition related information, information about whether HARQ-ACK istransmitted, HARQ-ACK repetition related information, etc. For example,the PHICH repetition related information may include all or part ofPHICH repetition number of times and PHICH bundle configuration/start SFinformation, PHICH resource allocation information correspondingthereto, etc. In addition, for example, the HARQ-ACK repetition relatedinformation may include all or part of HARQ-ACK repetition number oftimes and HARQ-ACK bundle configuration/start SF information, PUCCHresource allocation information corresponding thereto, etc.

The USS (or UE-specific RNTI) based PDCCH repetition related information(and corresponding PDSCH/PUSCH repetition related information) may alsobe independently configured for each DCI format type or DCI payloadsize. For example, independent repetition related information may beconfigured for TM-common DCI format (e.g., DCI format 0/1A) and DLTM-dedicated DCI format (e.g., DCI format 1/1B/1D/2/2A/2B/2C/2D) and ULTM-dedicated DCI format (e.g., DCI format 4).

In addition, as described above, the PRACH resource or the PRACHresource set may be allocated to correspond to different coverageenhancement requirements (e.g., measured path-loss or requiredSNR/SINR), and corresponding Msg3 transmission related information(Msg3-info) may be differently (or independently) configured for thePRACH resource or the PRACH resource set. The UE may select/transmit aspecific PRACH resource according to a coverage condition of the UE andthen perform a Msg3 transmitting operation and a PHICH receivingoperation corresponding thereto appropriate to Msg3 transmission relatedinformation (Msg3-info) that is configured/associated with thecorresponding specific PRACH resource.

The PUSCH transmission related information may be signaled/configured inthe same/similar way (e.g., for each PRACH resource (set) and/orcoverage enhancement requirement) by generalizing Msg3-info orirrespective of Msg3-info. For example, the UE may perform a PUSCHtransmitting operation appropriate for PUSCH transmission relatedinformation corresponding to a coverage condition of the UE withreference to the PUSCH transmission related information. The PUSCHtransmission related information may include all or part of, forexample, PUSCH repetition number of times and PUSCH bundleconfiguration/start SF information, information about whether a PHICH istransmitted, and/or PHICH repetition number of times/bundle information.

Similarly to the above description, the UE may skip (adetection/reception operation of a PHICH and) a PHICH based non-adaptiveautomatic retransmitting operation and perform only UL grant basedadaptive retransmission until receiving signaling for actual PHICHtransmission related information setting in a coverage-limitedsituation.

Method for Configuring RAR Window

In a legacy system (e.g., LTE-A system), a start subframe (SF) of an RARwindow may be determined as SF timing obtained by adding a specific SFoffset (e.g., three subframes) to SF timing at which PRACH preambletransmission ends. A size of the RAR window may be configured as a valuesignaled via SIB and may be, for example, 2, 3, 4, 5, 6, 7, 8, or 10subframes. The RAR window size may be defined as Nw. Accordingly, whenrepetition is applied to PRACH and/or RAR-PDCCH and/or RAR transmission,start SF and size of an RAR window corresponding thereto needs to bedetermined in consideration of a repetition number of times and/or abundle interval of each channel. When a bundle of a specific channeldoes not include consecutive SFs, a bundle interval (or the number ofSFs in a bundle) may be greater than a repetition number of times.

First, an RAR window start SF may be determined based on SF timing atwhich last PRACH preamble transmission of a PRACH bundle ends. Forexample, the RAR window start SF may be determined as SF timing (this isassumed as SF #K) obtained by adding a specific SF (e.g., 3 SFs) to alast PRACH preamble transmission subframe of a PRACH bundle. As anotherexample, the RAR window start SF may be determined as closest(available) RAR-PDCCH bundle start SF timing (or closest (available) RARbundle start SF timing) after the corresponding SF #K including SF #K.

The RAR window size may be determined based on an entire interval (whichis defined as Ba) in which an RAR-PDCCH bundle and an RAR bundlecorresponding thereto can be transmitted. An entire duration (Ba)corresponding to the RAR window size may correspond to a correspondingSF duration from initial RAR-PDCCH transmission time (of an RAR-PDCCHbundle) to last RAR transmission time (of an RAR bundle correspondingthereto) and may refer to (Nd+Nr) SF durations. For example, Ba may havea form of max(Nd, Nr)+a1 or Nd+Nr+a2, and in this case, max(Nd, Nr) mayrefer to a greatest value of Nd and Nr, a1 may refer to a positiveinteger in addition to 0, and a2 may refer to a positive integer inaddition to −1 and 0. As another example, the final RAR window size maybe determined based on a value obtained by adding Nw signaled via SIB toBa or a value obtained by multiplying Ba by Nw signaled via SIB ordetermined based on a duration including Nw (available) Ba.

Alternatively, the RAR window size may be determined based on anRAR-PDCCH bundle transmission duration (which is defined as Bd) and anRAR bundle transmission duration (which is defined as Br). The RAR-PDCCHbundle transmission duration Bd may refer to a corresponding SF durationfrom initial RAR-PDCCH transmission time corresponding to one RAR-PDCCHbundle to last RAR-PDCCH transmission time, and refer to, for example,(Nd+b) SF durations where b is a positive integer in addition to 0. TheRAR bundle transmission duration Br may refer to a corresponding SFduration from initial RAR (PDSCH) transmission time corresponding to oneRAR bundle to last RAR (PDSCH) transmission time and refer to, forexample, (Nr+b) SF durations. As another example, the last RAR windowsize may be determined based on a value (Bd×Nw+Br) obtained bymultiplying Bd by Nw and adding Br to the resultant value or determinedbased on a value (Bw+Br+a where a is an integer equal to or greater than0) obtained by adding an RAR bundle interval Br corresponding to a lastRAR-PDCCH bundle to a duration (defined as Bw) including Nw (available)Bd.

As another method, similarly to the above description, aseparate/independent RAR window size (or a specific parameter value usedto determine the same) may be configured for each respective PRACHresource or PRACH resource set, and the RAR window size (or a specificparameter value used to determine the same) may be signaled/configured((specific) SIB) while included in RAR-info.

The case in which multiplexing (e.g., code division multiplexing (CDM)and/or time division multiplexing (TDM) and/or frequency divisionmultiplexing (FDM)) is applied between PRACH transmission of anormal-coverage UE (to which repetition is not applied) and PRACH bundletransmission of a coverage-limited UE (to which repletion is applied)and/or between PRACH bundle transmission with different repetitions maybe considered. In this case, (in order to differentiate PRACH signalsfrom a plurality of UEs to be overlapped) a repetition number of timesNp corresponding to a PRACH (bundle) signal transmitted from the UE(i.e., received from an eNB) may be transmitted/signaled while includedin RAR (or RAR-PDCCH), and/or, time and/or frequency resourceinformation associated with corresponding PRACH (bundle) signaltransmission may be transmitted/signaled while included in RAR (orRAR-PDCCH). For example, the time and/or frequency resource informationassociated with the PRACH (bundle) signal transmission may includestart/configuration SF (timing) information (and/or SFN informationcorresponding thereto) of the PRACH bundle signal and/or frequency bandinformation (e.g., index in the frequency domain) for transmitting aPRACH signal, etc.

FIG. 9 is a diagram illustrating an example of a method according to thepresent invention.

Referring to FIG. 9, a UE may transmit a PRACH signal using a specificPRACH resource in operation S902. As described above, the PRACH resourcemay refer to a combination of sequence/subframe SF/frequency band, etc.used to transmit a PRACH preamble. In addition, a PRACH resource or aPRACH resource set may be allocated to correspond to different coverageenhancement requirements, and the UE may select a specific PRACH andtransmit a PRACH signal according to a coverage condition (e.g.,measured path-loss value or coverage enhancement requirements (e.g., SNRor SINR) calculated based thereon) of the UE. For example, the PRACHsignal may be allocated to a PRACH preamble.

In operation S904, the UE may receive an RAR signal in a specific timeperiod (e.g., RAR window) in response to the PRACH signal transmitted inoperation S902. When the UE is a first type UE (or a normal-coverage UEor a UE to which repetition is not applied), the UE may receive an RARsignal at subframe timing obtained by adding a specific SF offset (e.g.,3) to a subframe in which the PRACH signal is transmitted in operationS902. In this case, the RAR window size may be configured as a valuesignaled via SIB and may be, for example, 2, 3, 4, 5, 6, 7, 8, or 10subframes.

On the other hand, when the UE is a second type UE (or an LCT UE, a UEwith a limited coverage, or a UE to which repetition is applied), the UEmay repeatedly transmit a PRACH signal during a PRACH bundle and mayreceive/detect an RAR signal in a duration corresponding to the RARwindow size in the RAR window start SF according to the presentinvention. In this case, the RAR window start SF may be determined assubframe timing obtained by adding a specific subframe offset (e.g., 3)to a last PRACH signal transmission subframe of a PRACH bundle ordetermined as closest RAR-PDCCH bundle start SF timing (or closest RARbundle start SF timing) after the determined subframe.

When the UE is a second type UE, the RAR window size may be determinedbased on an entire duration (which is defined as Ba) in which anRAR-PDCCH bundle and an RAR bundle corresponding thereto can betransmitted (e.g., max(Nd, Nr)+a1 or Nd+Nr+a2) or determined asRAR-PDCCH bundle transmission duration (which is defined as Bd) and anRAR bundle transmission duration (which is defined as Br) (e.g.,Bd×Nw+Br or Bw+Br+a).

In consideration of multiplexing applied between PRACH transmission of afirst type UE and a second type UE or PRACH transmission of a secondtype UE, the RAR signal received in operation S904 may includeinformation about a repeated transmission number of times Np of thePRACH signal transmitted in operation S902. Additionally or separately,the RAR signal of operation S904 may include time and/or frequencyresource information associated with PRACH signal transmission ofoperation S902. The UE may differentiate PRACH signals from a pluralityof UEs to be overlapped using these information items.

Although not illustrated in FIG. 9, the UE may receive downlink controlinformation (or a PDCCH signal) for scheduling the RAR signal. In thiscase, the downlink control information (or a PDCCH signal) may be masked(or scrambled) with RA-RNTI information. Hereinafter, a method fordetermining RA-RNTI information will be described.

Method for Determining RA-RNTI

In a legacy system (e.g., a LTE-A system), an RA-RNTI value may bedetermined according to a function of SF timing (which is defined asT_id) in which PRACH preamble transmission is started and an index(which is defined as F_id) on the frequency domain of the correspondingPRACH preamble. For example, the RA-RNTI value may be determinedaccording to RA-RNTI=1+T_id+10×F_id. Accordingly, when repetition isapplied to PRACH transmission, an RA-RNTI value corresponding theretoneeds to be determined in consideration of a repetition number of timesof a PRACH and/or a bundle interval.

When repetition is applied to PRACH transmission, T_id may be determinedas SF timing in which initial PRACH preamble transmission of a PRACHbundle is started or SF timing in which last PRACH preamble transmissionends. F_id may be determined as an index in the frequency domain of aPRACH preamble (i.e., an initial or last PRACH preamble of a PRACHbundle) transmitted through the corresponding T_id. In addition, amethod for determining an RA-RNTI value according to a PRACH repetitionnumber of times Np (in addition to T_id and F_id). Accordingly,according to the present invention, the RA-RNTI value may be determinedaccording to a function of Np. In more detail, when PRACH preambletransmission related information (e.g., PRACH transmission SF timingT_id and/or index F_id in the frequency domain) is the same, the RA-RNTIvalue be differently determined according to a value Np.

In addition, when a situation in which respective PRACH resource (sets)coexist/contend with each other based on different (various)transmission timing and repetition number of times is considered, it maynot be easy to differentiate an RA-RNTI according to T_id and/or F_id(in particular, T_id). Accordingly, when repetition is applied to PRACHtransmission, T_id (and/or F_id) may be determined/configured as notbeing used to determine the RA-RNTI value.

When PRACH bundle transmission (e.g., a PRACH preamble is repeatedlytransmitted) is applied, timing in which (initial) PRACH preambletransmission is started may be configured using a system frame number(SFN) (and/or PRACH repetition number of times Np or a subframe durationincluding one PRACH repetition (e.g., a duration from a subframe inwhich an initial PRACH preamble is transmitted to a subframe in which alast PRACH preamble is transmitted)) and an SF number/index as aparameter by considering that a PRACH transmission duration is extended(over a plurality of radio frames) due to repetition. For example,timing at which transmission of a specific PRACH preamble bundle isstarted may be configured as SFN #N (and a specific SF number/index inthe corresponding SFN), and timing at which transmission of anotherPRACH preamble bundle is started may be configured as SFN #M (and aspecific SF number/index in the corresponding SFN) different from SFN#N. In addition, an RA-RNTI (or T_id for determining the same) value mayalso be determined according to a function of an SFN (and/or an SFnumber/index) corresponding to a time point at which (initial or last)PRACH preamble transmission is started/ended in consideration of a PRACHbundle transmission duration (which is extended over a plurality ofradio frames).

In addition, in consideration of the case in which code divisionmultiplexing (CDM) is applied between PRACH transmission of anormal-coverage UE (to which repetition is not applied) and PRACH bundletransmission of a coverage-limited UE (to which is applied) and/orbetween PRACH bundle transmission with different repetitions, an RA-RNTIvalue may be determined according to a function of a root sequence index(or a combination of a root sequence index and a cyclic shift value) ofa PRACH signal corresponding to the RA-RNTI value.

As another method, an independent dedicated RA-RNTI value may bedetermined/configured for each PRACH resource or PRACH resource set.Accordingly, the RA-RNTI value may be pre-determined (irrespective of aT_id and/or F_id value) without the above separate calculationprocedure. The independent dedicated RA-RNTI value may besignaled/configured (via (specific) SIB) for each PRACH resource orPRACH resource set while included in RAR-info.

PRACH Transmission for Scheduling Request

In a legacy system (e.g., LTE-A system), when a scheduling request (SR)is present, if a PUCCH resource for SR use is pre-allocated, a UE maytransmit a (positive) SR signal using the corresponding PUCCH resource,or otherwise, the UE may select and transmit an arbitrary PRACH preambleto perform scheduling request. In a coverage-limited environment (or asituation in which various UL channel/signals including a PRACH arerepeatedly transmitted), assuming that a separate PUCCH resource for SRuse is not allocated to the UE, if scheduling request is present, thecorresponding UE may select and transmit an arbitrary PRACH resource (byas much as a repetition number of times corresponding to thecorresponding PRACH resource) similarly to a legacy case among aplurality of PRACH resource (sets) with different repetition numbers.However, 1) when performance of the selected PRACH resource (repetitioncorresponding thereto) is lower than coverage enhancement requirementsrequired for a corresponding UE, additional PRACH retransmission mayrequired, and 2) when performance of the selected PRACH resource(repetition corresponding thereto) is much higher than the coverageenhancement requirements required for the corresponding UE, many PRACHresources may be unnecessarily consumed, thereby causing unnecessaryoverhead and/or interference in terms of use of UL resource.

Accordingly, in a coverage-limited situation, when the UEselects/transmits a (repetition based) PRACH for use of schedulingrequest, a PRACH resource may be selected as follows.

-   -   A PRACH resource corresponding to RAR that is successfully        received among PRACH resources that have been        selected/transmitted by the corresponding UE in an initial        random access procedure (or (contention-based) random access        procedure) that has been most recently (lastly) performed, or    -   An arbitrary PRACH resource set with the same repetition number        of times as a PRACH resource corresponding to RAR that is        successfully received, or    -   An arbitrary PRACH resource set with a smallest repetition        number of times greater than a corresponding repetition number        of times (or a greatest repetition number of times less than the        corresponding repetition number of times) (when a PRACH resource        set with the corresponding repetition number of times is not        present).

As another method, a method for separately allocating a PRACH resourceand transmission related information (e.g., a corresponding repetitionnumber of times and/or bundle start/configuration SF, etc.) to be usedfor scheduling may be considered.

FIG. 10 is a flowchart illustrating an example of a method according tothe present invention. In the example of FIG. 10, it is assumed that aplurality of PRACH resource (sets) is preconfigured for transmission ofa PRACH signal, different repetition numbers are preconfigured withrespect to a plurality of PRACH resource (sets), and a UE selects aPRACH resource among the plurality of preconfigured PRACH resource(sets) and transmits a PRACH signal (by as much as a repetition numberof times corresponding to the corresponding PRACH resource).

Referring to FIG. 10, in operation S1002, in order to perform an initialrandom access procedure (or a most recent random access procedure), theUE may repeatedly transmit a first PRACH signal using a first PRACHresource (by as much as a repetition number of times corresponding tothe first PRACH resource). Then, in operation S1004, the UE maysuccessfully receive an RAR signal for the first PRACH signal.

In operation S1006, the UE may transmit a second PRACH signal forscheduling request. In this case, a PRACH resource for transmission ofthe second PRACH signal for scheduling request may be determined basedon the first PRACH signal for an RAR signal that is successfullyreceived, as described above.

For example, when the first PRACH resource corresponds to one of aplurality of preconfigured PRACH resource (sets), the second PRACHsignal may be repeatedly transmitted by as much as a repetition numberof times configured for the first PRACH resource using the first PRACHresource.

As another example, when a repetition number of times of the first PRACHsignal corresponds to one of a preconfigured repetition number of timesfor a plurality of PRACH resource (sets), the second PRACH signal may berepeatedly transmitted by as much as a repetition number of times of thefirst PRACH signal using a PRACH resource corresponding to therepetition number of times of the first PRACH signal.

As another example, when the first PRACH resource does not correspond toa plurality of PRACH resource (sets) and a repetition number of times ofthe first PRACH signal does not correspond to a preconfigured repetitionnumber of times with respect to a plurality of PRACH resource (sets),the second PRACH signal may be transmitted using a PRACH resourcecorresponding to a smallest repetition number of times (or a greatestrepetition number of times less than a repetition number of times of thefirst PRACH signal) greater than a repetition number of times of thefirst PRACH signal among a plurality of PRACH resources.

In the case of PRACH transmission performed according to indication(e.g., reception of a PDCCH order, etc.) from an eNB, a PRACH resourceand transmission related information (e.g., corresponding repetitionnumber of times and/or bundle start/configuration SF, etc.) similarly tothe above case, and/or (when the PRACH resource and transmission relatedinformation are referred to as “PRACH-rep info set” for convenience), aplurality of PRACH-rep info sets with different PRACH repetition numbersmay be configured, and when a UE first transmits a PRACH bundle with asmallest repetition number of times (for example, when a PDCCH order isreceived) based on the PRACH-rep info sets and fails to receive/detectRAR corresponding to the PRACH bundle (e.g., a PDCCH order isre-received), PRACH repetition number of times may be increased using amethod for transmitting a PRACH bundle with a second smallest repetitionnumber of times. As another method, (when one or more PRACH-rep infosets are preconfigured), a repetition number of times (or informationcorresponding thereto) for PRACH bundle transmission may be directlyindicated through a PDCCH order.

(By generalizing the above proposal) when a method for selecting a PRACHresource corresponding to PRACH repetition number of times which RAR issuccessfully received in an initial access or recent random accessprocedure) is defined as Method 1, a method for selecting a PRACHresource corresponding a PRACH repetition number of times that isseparately allocated through a higher layer signal (such as(UE-specific) RRC signaling except for SIB), a PDCCH (order) signal,etc. is defined as Method 2, a method for selecting a PRACH resourcecorresponding to a smallest repetition number of times among PRACHsconfigured for SIB is defined as Method 3, and a method for selecting aPRACH resource corresponding to a repetition number of times that isestimated based on specific measurement (e.g., reference signal receivedpower (RSRP)) among PRACHs configured for SIB is defined as Method 4,whether Method 1 or another method (Method 2, 3, or 4) is applied duringtransmission of a PRACH (in an RRC connected mode) and/or whether Method3 or Method 4 is applied may be configured for the UE (using a UE-commonor UE-specific method).

In the case of the above methods (e.g., Method 3 or 4), differentmethods may be applied according to a step/time/situation at which arandom access produce is performed. For example, whether the randomaccess is random access in initial access and RRC idle mode or randomaccess in an RRC connected mode, different methods may be applied. Forexample, in an RRC idle mode (including initial access), there is thepossibility that latency increment and/or accuracy degradation withrespect to measurement (e.g., RSRP) (in terms of average-sense) over aplurality of SF durations in consideration of a coverage-limitedsituation in which an operation is performed based on repetition isrelatively increased. Accordingly, Method 3 may be applied to the caseof a random access procedure in an RRC idle mode (including initialaccess) (or only to initial access). On the other hand, Method 4 may beapplied to the case of a random access procedure in an RRC connectedmode in which a burden of measurement latency/accuracy is relatively low(or the remaining cases except for initial access).

Support of Different Coverage Enhancement (CE) Between DL/UL

In the case of some UEs, DL coverage and UL coverage may be differ. Forexample, some UEs may require repeated application for transmission of aUL channel/signal in order to ensure a proper level of ULperformance/operation with respect to the UL coverage (which is referredto as a “UL CE mode”) but may ensure a proper level of DL receptionperformance/operation without repeated application to transmission of aDL channel/signal with respect to the DL coverage (which is referred toas a “DL non-CE mode”). In the case of these UEs, it may be effective interms of overall system overhead/latency to preconfigured relatedinformation/parameters so as to apply repetition to transmission of a ULchannel/signal (e.g., PRACH and/or Msg3) in an initial access procedureover a plurality of SFs but to support an operation (i.e., a combinationof a UL CE mode and a DL non-CE mode) for one timetransmission/reception through only one SF without repetition like aconventional case in the case of a DL channel/signal (e.g., RAR and/orMsg4).

In addition, when repetition is performed for coverage enhancement,since a PDCCH can also be repeated, cross-SF scheduling may be used. Thecross-SF scheduling may refer to a case in which data transceiving and agrant information transceiver for the same are performed in differentsubframes. For example, when a last PDCCH in a PDCCH bundle istransmitted in SF #n, a start PDSCH in a PDSCH may be transmitted in SF#(n+1). When a repetition number of times is 1, the case in whichcross-SF scheduling is not used may be considered. For example, when aPDCCH bundle size is 1, the UE may assume that the cross-SF schedulingis not used. The cross-SF scheduling is one example, and the UE mayassume the case in which a PDCCH bundle size is 1 or a bundle size forDL channel/signals is 1 differently from the case in which a bundle sizeis greater than 1. This may be specific to a situation in which acoverage enhancement mode is enabled when a bundle size of transmissionof a UL channel/signal is greater than 1.

As a method for determining a UE that can operate using this method byan eNB, RAR (and/or Msg4) corresponding to a specific PRACH (and/orMsg3) resource configured with a repetition number of times equal to orgreater than 2 and a PDCCH repetition number of times correspondingthereto may be configured to 1 (i.e., to be transmitted once withoutrepetition like in a conventional case) via second-type-dedicated SIB.Accordingly, when a UE that receives the correspondingsecond-type-dedicated SIB performs PRACH preamble transmission using acorresponding specific PRACH resource, transmission of RAR (and/or Msg4)corresponding thereto may be performed for reception through one SF likein a conventional case without repetition according to setting ofcorresponding second-type-dedicated SIB. In this case, receptiontiming/duration for RAR (e.g., RAR window start/configuration SF) mayalso apply a conventional method or may configure a method to be appliedamong a conventional method or a CE mode method (to which a repetitionnumber of times of 1 is applied). In this case, a method by which the UEoperates may be determined according to timing or a repetition number oftimes in which RAR is transmitted. For example, when an SF in which RARis transmitted corresponds to an SF that cannot be used in the case oftransmission using a coverage enhancement mode method, this means thatthe RAR is transmitted in a normal coverage mode, and thus it may beassumed that the UE may operate in a normal coverage mode. As anothermethod, a CE mode or a conventional method may be determined accordingto whether cross-SF scheduling is applied. In addition, a mode in whichthe UE operates among a coverage enhancement mode and a normal coveragemode may be signaled in RAR or may be configured together when PRACHrepeated level/number of times is configured for SIB.

As another method, a second-type-dedicated PRACH resource (e.g., with arepetition number of times of 2 or more) to which repeated transmissionis applied may be configured (irrespective of a legacy PRACH resource towhich repetition is not applied) through a legacy SIB. In this case, aUE that performs PRACH preamble transmission using the correspondingsecond-type-dedicated PRACH resource configured for the legacy SIB mayoperate so as to receive RAR (and/or Msg4) corresponding to thesecond-type-dedicated PRACH resource and PDCCH transmissioncorresponding thereto through one SF (without repetition) like in aconventional case. In this case, a conventional method may also beapplied to reception timing/duration (e.g., RAR windowstart/configuration SF) for the RAR or a method among a conventionalmethod and a CE mode method (to which a repetition number of times of 1is applied) may be configured. In this case, the UE may determine amethod by which the UE operates may be determined according to timing ora repetition number of times in which RAR is transmitted. For example,when an SF in which RAR is transmitted is an SF that cannot be used inthe case of transmission using a coverage enhancement mode method, thismeans that the RAR is transmitted in a normal coverage mode, and thus itmay be assumed that the UE may operate in a normal coverage mode. Asanother method, a CE mode or a conventional method may be determinedaccording to whether cross-SF scheduling is applied. In addition, a modein which the UE operates among a coverage enhancement mode and a normalcoverage mode may be signaled in RAR or may be configured together whenPRACH repeated level/number of times is configured for SIB.

A UE to which repetition based coverage enhancement is applied in orderto reduce a burden of use of a receiving buffer of the UE may beconfigured such that a PDCCH repeated transmission duration and a PDSCHrepeated transmission duration corresponding thereto may not overlapeach other. This configuration may be referred to as “cross-SFscheduling”. In this case, even if repetition is exceptionally appliedto UL transmission with respect to a UE to which a combination of a ULCE mode and a DL non-CE mode is applied, a conventional method (i.e., amethod for transmitting a PDCCH and a PDSCH corresponding theretothrough one SF) may be applied to DL transmission without change. Amethod for transmitting grant information (or PDCCH) and data (or PDSCH)scheduled by the same through the same SF may be referred to as “same-SFscheduling”. As another method, a method to be applied to thecorresponding UE among the cross-SF scheduling method and the same-SFscheduling method may be pre-signaled (through an SIB, etc.). As anothermethod, a method to be applied to a corresponding UE by default amongthe above two methods (the cross-SF scheduling method and the same-SFscheduling method) may be pre-defined or a method to be applied to theUE may be changed/configured via additional specific signaling (e.g.,UE-specific RRC signaling) while operating in a mode configured via SIB,etc.

Configuring a Plurality of DL CE Levels to Single UL CoverageEnhancement (CE)

As another method, in a situation in which a corresponding PRACHrepetition number of times (and/or Msg3 repetition number of times,etc.) is independently (or differently) configured for each UL coverageenhancement requirement (which is referred to as a UL CE level, forconvenience), a setting method for corresponding a plurality ofdifferent DL CE levels (e.g., RAR repetition number of times and/or Msg4repetition number of times, etc.) to one UL CE level may be consideredin order to support the above various (or different) UL/DL CE levelcombinations. Here, a repetition number of times, configuration SFinformation, etc. which are applied to transmission of UL channel/signal(e.g., PUSCH and/or PUCCH) as well as PRACH (and/or Msg3) maycorrespond/be configured to each UL CE level, and a repetition number oftimes, configuration SF information, etc. which are applied totransmission of a DL channel/signal (e.g., PDCCH and/or PDCCH) as wellas RAR (and/or Msg4) may correspond/be configured to each DL CE level.On the other hand, a method for configuring a plurality of different ULCEs as corresponding to one DL CE level may also be used.

For example, a plurality of (e.g., 2) RAR repetition number of timesNr_1 and Nr_2 may be configured to correspond to a PRACH repetitionnumber of times Np corresponding to one specific UL CE level. The UE mayperform Np repeated transmissions on a corresponding PRACH and thenperform an RAR reception/detection operation while assuming each of twocorresponding RAR repetition number of times (i.e., Nr_1 and Nr_2) todetermine a final Nr value corresponding to RAR that is successfullyreceived/detected (among Nr_1 and Nr_2) as a DL CE level of the UE.Then, DL channel/signal repetition configuration corresponding theretomay be applied and then a DL reception operation may be performed. Inthis case, when RAR reception/detection is simultaneously successfulwith respect to a plurality of repetition numbers, the UE may determinerepetition configuration corresponding to a smallest value among thecorresponding plurality of RAR repetition numbers as a DL CE level ofthe UE. Repetition corresponding to a smallest value may be determinedas a DL CE level of the UE. It may be preferable in terms of DL resourceoverhead to determine repetition configuration corresponding to asmallest value as a DL CE level. For convenience of description, aprocedure for performing an RAR reception/detection operation on aplurality of repetition numbers and applying DL channel/signalrepetition configuration corresponding to RAR that is successfullyreceived/detected is referred to as “RAR blind decoding (BD)”.

As another method for configuring a plurality of DL CE levels ascorresponding to one UL CE level, a PRACH repetition number of times(and UL repetition number of times and transmission SF configurationinformation including the same) may be configured so as to differentiatePRACH preamble resources (applied repetition number of times are thesame) corresponding to respective DL CE levels in a state in which thesame PRACH repetition number of times corresponds/is configured to thecorresponding plurality of DL CE levels in time/frequency/code. On theother hand, as another method for configuring a plurality of UL CElevels as corresponding to one DL CE level, an RAR repetition number oftimes (and a DL repetition number of times including the same andtransmission SF configuration information) may be configured such thatan RAR (and/or PDCCH for scheduling the same) transmission resourcecorresponding to each UL CE level is differentiated in terms oftime/frequency/code rate, etc. while the same RAR repetition number oftimes is configured to correspond/be configured to the correspondingplurality of UL CE levels.

A PRACH power ramping method with respect to a case in which a pluralityof DL CE levels corresponds/is configured to a single UL CE level may beperformed by sequentially applying one calculated UE transmit powervalue to all PRACH resources corresponding to one PRACH repetitionnumber of times and then sequentially re-applying (one) ramping-up UEpower to all PRACH resources. In this case, an order for applying one UEtransmit power to a plurality of PRACH resources may be from a low levelto a high level of a corresponding DL CE level (e.g., DL channel/signalrepetition number of times).

For example, a plurality of (e.g., 2) PRACH resources 1 and 2 allocatedto one PRACH repetition number of times Np may correspond to differentRAR repetition numbers Nr_1 and Nr_2 (e.g., Nr_1<Nr_2). Assuming thatinitial (first) UE transmit power is Pu and next (second) UE power afterpower ramping is applied is Pu+Pr, a corresponding UE may first performPRACH transmission by applying power value Pu to PRACH resource 1corresponding to a low value Nr_1, may perform PRACH transmission byre-applying a power value Pu to PRACH resource 2 corresponding to a nexthigh value Nr_2 (when RAR fails), and then may perform sequent PRACHtransmission by applying Pu+Pr to PRACH resource 1, applying Pu+Pr toPRACH resource 2, applying Pu+2Pr to PRACH resource 1, and applyingPu+2Pr to PRACH resource 2 (until RAR is successfully received).

As another method for configuring a plurality of DL CE levels ascorresponding to one PRACH repetition level (and UL repetition number oftimes and transmission SF configuration information including the same),when different PRACH resources (with the same repetition number oftimes, which are differentiated in time/frequency/code) correspond/areconfigured for respective transmission power values/ranges (orinformation for deriving the same) of a UE, which are used for a PRACHsignal, different DL CE levels may be applied according to transmitpower and/or transmitting resource used for PRACH signal transmission toperform a DL reception operation.

For example, (when transmit power of a UE is Pu), different UE transmitpower ranges Pu-range 1 (e.g., X≤Pu<Y) and Pu-range 2 (e.g., Y≤Pu<Z) maycorrespond to a plurality of (e.g., 2) PRACH resources 1 and 2 allocatedto one PRACH repetition number Np, respectively. In addition, differentRAR repetition numbers Nr_1 and Nr_2 may correspond to a correspondingplurality ogyorf PRACH resources 1 and 2 (or Pu-ranges 1 and 2),respectively. Accordingly, Pu that is determined by applying initialpower setting, PRACH power ramping, and the like (based on measuredpath-loss, etc.) is within Pu-range 1, a UE may perform transmissionthrough PRACH resource 1 corresponding to Pu and then perform an RARreception/detection operation assuming a repetition number of timesNr_1. When Pu is within Pu-range 2, the UE may perform transmissionthrough PRACH resource 2 corresponding to Pu and then perform an RARreception/detection operation assuming a repetition number of timesNr_2.

In addition, when one or more DL CE levels are configured to correspondto one PRACH repetition level (and UL repetition number of times andtransmission SF configuration information including the same), differentPRACH resource may correspond/be set for respective transmit powervalues/ranges (or information for deriving the same) of a UE, which isused for a PRACH signal) so as to use different PRACH resourcesaccording to transmit power applied to the PRACH signal. In the case ofdifferent PRACH resources, applied repetition number of times are thesame but can be differentiated in time/frequency/code, and differentPRACH resources may be used according to transmit power applied to aPRACH signal without separate correspondence/setting from a DL CE level.A DL CE level for a corresponding UE may be determined through RAR BDand/or then may be configured/reconfigured through an appropriateprocedure.

In addition, when one or more DL CE levels are configured to one PRACHrepetition level (and UL repetition number of times and transmission SFconfiguration information including the same), the corresponding UE mayreport transmit power information (or information for deriving the same)of a UE, which is used in PRACH (repeated) transmission corresponding toreceived/detected RAR directly to an eNB through Msg3 transmission (ornext PUSCH transmission) (in a situation without separatecorrespondence/setting between the aforementioned PRACH transmitpower/resources or a situation in which corresponding setting is given).The eNB may appropriately re-set a next UL CE level (e.g., ULchannel/signal repetition number of times) to be applied to thecorresponding UE based on the reported transmit power information. Inthis case, a DL CE level for the corresponding UE may also be determinedthrough RAR BD and/or may be set/re-set through an appropriateprocedure.

In all of the methods, in the case of different PRACH resources with thesame repetition number of times, which are differentiated intime/frequency/code, independent (different) UL channel/signal (e.g.,PUSCH and/or PUCCH (as well as Msg3)) repetition number of times andtransmission SF configuration information may be correspond to thedifferent PRACH resources. A UE that succeeds in RAR reception/detectioncorresponding to specific PRACH resource transmission may apply ULrepetition information corresponding/set to a corresponding specificPRACH resource with respect to next UL transmission (as well as Msg3).

Method for Identifying and Supporting Second Type UE

As described above, for a coverage-limited UE (or a UE configured toperform repeated transmission for CE), a separate PRACH resource(referred to as a CE PRACH resource) (which applies repeatedtransmission) which can be differentiated from a legacy PRACH resourceused by a legacy UE may be configured. In addition, for PRACH repeatedtransmission appropriate for a plurality of CE levels, different CEPRACH resources may be allocated for respective CE levels (which applydifferent repetition numbers and/or can be differentiated inCDM/TDM/FDM, etc.).

According to technologies for low-cost/low-specifications of a secondtype UE, reduction in the number of reception antennas, reduction in amaximum TB size, reduction in a reception buffer size, etc. may beconsidered. In particular, the reception buffer size may be achieved byreducing a frequency duration/range of a reception target (e.g., bylimiting only a small number of specific RBs). In the case of variouscontrol channels (e.g., PCFICH, PHICH) as well as a PDCCH, RE/REG/CCE,etc. constituting the control channel may be transmitted over an entiresystem BW through a series of procedures such as interleaving, and thusit may be difficult to reduce a reception frequency duration/range(i.e., a reception bandwidth) with respect to the corresponding controlchannel. On the other hand, in the case of a PDSCH as a data channel,RE, and the like constituting the PDSCH may be limitedly transmittedonly to a specific frequency resource (e.g., specific RB region)according to scheduling of an eNB, and thus a reception bandwidth (e.g.,RB number) for the PDSCH may be reduced so as to reduce a received databuffer size. For convenience, a second type UE withlow-cost/low-specifications, which can be achieved according to thistechnology, may be referred to as a “low-cost UE”, (maximum) datascheduling/reception (available) bandwidth allocated to the low-cost UEmay be referred to as “scheduling bandwidth (BWLC)”, and datatransmission scheduled for an actual low-cost UE may be limited to RBsbelonging to the corresponding scheduling bandwidth.

In order to support the low-cost UE, an eNB (may identify/recognize thecorresponding low-cost UE and) may need scheduling so as totransmit/receive a PDSCH corresponding to RAR and Msg4 through only RBsin a scheduling bandwidth BWLC from an RACH procedure for initialaccess. To this end, a separate PRACH resource (referred to as an LCPRACH resource) differentiated from a legacy PRACH resource may bere-configured for the low-cost UE such that an eNB may performscheduling of RAR/Msg4 corresponding to LC PRACH resource transmission(from the low-cost UE) within only a scheduling bandwidth BWLC. However,when a coverage-limited low-cost UE (referred to as a CE LC UE) thatrequires PRACH repeated transmission is also considered, different CEPRACH resources (referred to as CE LC PRACH resources) differentiatedfor respective CE levels may be allocated similarly to the abovedescription. However, allocation of the CE LC PRACH may cause depletionof PRACH transmitting resources and degradation in PRACH receptionperformance in terms of an entire system due to excessive PRACH resourcedimensioning.

As one method for this, a method for setting a separate LC PRACHresource differentiated from a legacy PRACH resource only for a non-CELC UE and commonly setting a CE PRACH resource for each CE level for allCE UEs (including an LC UE and any UE that is not the LC UE) thatrequire CE may be considered. In addition, the corresponding LC PRACHresource setting information may include scheduling bandwidthinformation for scheduling corresponding RAR and/or Msg4. Similarly, thecorresponding CE PRACH resource setting information (for each CE level)may include scheduling bandwidth information for scheduling thecorresponding RAR and/or Msg4.

In the above method, in the case of the non-CE LC UE, the UE mayselect/transmit an LC PRACH resource such that an eNBidentifies/recognizes an LC type. On the other hand, in the case of theCE LC UE, the eNB cannot identity/recognize an LC type only byselecting/transmitting a CE PRACH resource by the UE, and thus the CE LCUE may notify the eNB that the UE is an LC type through Msg3. Inaddition, the eNB may differently allocate Msg3 transmitting resourcescorresponding to the two respective UE types (i.e., LC type or non-LCtype) to RAR (e.g., Msg3 transmitting resources may be allocated to usedifferent RBs and/or different DMRS cyclic shifts) so as toidentify/recognize a UE type according to a Msg3 receiving resource. Themethod may also be applied to the case in which a separate LC PRACHresource is not configured for a non-CE LC UE.

Thus far, the description has been given in terms of the case in whichrepeated transmission and reception are performed for coverageenhancement of a second type UE, but it may be understood that theprinciple according to the present invention is not restrictedly appliedonly to the repeated transmission and reception. In particular, thepresent invention may also be applied to the case in which repeatedtransmission and reception are not performed in the same/similar way.

The embodiments of the present invention described above arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim by asubsequent amendment after the application is filed.

FIG. 11 illustrates a BS and a UE to which the present invention isapplicable.

Referring to FIG. 11, a wireless communication system includes the BS1110 and the UE 1120. When the wireless communication system includes arelay, the BS 1110 or the UE 1120 may be replaced with the relay.

The BS 1110 includes a processor 1112, a memory 1114, and a radiofrequency (RF) unit 1116. The processor 1112 may be configured to embodythe procedures and/or methods proposed by the present invention. Thememory 1114 is connected to the processor 1112 and stores various piecesof information associated with an operation of the processor 1112. TheRF unit 1116 is connected to the processor 1112 and transmits/receives aradio signal. The UE 1120 includes a process 1122, a memory 1124, and anRF unit 1126. The processor 1122 may be configured to embody theprocedures and/or methods proposed by the present invention. The memory1124 is connected to the processor 1122 and stores various pieces ofinformation associated with an operation of the processor 1122. The RFunit 1126 is connected to the processor 1122 and transmits/receives aradio signal.

The embodiments of the present invention may be implemented by variousmeans, for example, hardware, firmware, software, or a combinationthereof. In a hardware implementation, an embodiment of the presentinvention may be implemented by one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSDPs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, etc.

In a firmware or software implementation, methods according to thepresent invention may be implemented in the form of a module, aprocedure, a function, etc which are configured to perform the functionsor operations as described in the present specification. Software codemay be stored in a computer-readable medium in the form of instructionsand/or data and may be executed by a processor. The computer-readablemedium is located at the interior or exterior of the processor and maytransmit and receive data to and from the processor via various knownmeans.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the scope of the invention. Thus, it is intendedthat the present invention cover the modifications and variations ofthis invention provided they come within the scope of the appendedclaims and their equivalents.

The present invention is applicable to a wireless communicationapparatus such as a user equipment (UE), a base station (BS), etc.

What is claimed is:
 1. A method for performing a random access procedureby a user equipment (UE) in a wireless communication system supportingcoverage enhancement, the method comprising: repeatedly transmitting, bythe UE, a physical random access channel (PRACH) signal; determining, bythe UE, a random access radio network temporary identifier (RA-RNTI)corresponding to the PRACH signal using system frame number (SFN)information, wherein time index information and frequency indexinformation are not used for determining the RA-RNTI; and monitoring, bythe UE, downlink control information masked by the determined RA-RNTI,wherein the time index information indicates a subframe starting therepeated transmission of the PRACH signal, the frequency indexinformation indicates a frequency index of the PRACH signal transmittedin the starting subframe, and the SFN information indicates a radioframe starting the repeated transmission of the PRACH signal.
 2. Themethod according to claim 1, wherein the monitoring the downlink controlinformation is performed in a random access response (RAR) window, theRAR window indicating a time interval for detecting the RA-RNTI andreceiving a random access response, and wherein a start subframe of theRAR window is determined by adding a specific subframe offset to asubframe ending the repeated transmission of the PRACH signal.
 3. Themethod according to claim 2, wherein the specific subframe offset is 3subframes.
 4. The method according to claim 1, wherein a number ofrepetitions for transmitting the PRACH signal is determined based on areference signal received power (RSRP) measurement.
 5. The methodaccording to claim 1, further comprising: receiving system informationcomprising information about random access response (RAR) window sizes,the RAR window sizes being independently configured for a plurality ofPRACH resources configured for the UE, wherein a size of the RAR windowis determined as a RAR window size configured for a PRACH resource usedfor transmitting the PRACH signal.
 6. The method according to claim 1,wherein a time interval for the repeated transmission of the PRACHsignal is extended over a plurality of radio frames.
 7. The methodaccording to claim 6, wherein each radio frame comprises 10 subframes.8. A user equipment (UE) for performing a random access procedure in awireless communication system supporting coverage enhancement, the UEcomprising: a transceiver; and a processor operatively connected to thetransceiver and configured to: control the transceiver to repeatedlytransmit a physical random access channel (PRACH) signal, determine arandom access radio network temporary identifier (RA-RNTI) correspondingto the PRACH signal using system frame number (SFN) information, whereintime index information and frequency index information are not used fordetermining the RA-RNTI, and monitor downlink control information maskedby the determined RA-RNTI, wherein the time index information indicatesa subframe starting the repeated transmission of the PRACH signal, thefrequency index information indicates a frequency index of the PRACHsignal transmitted in the starting subframe, and the SFN informationindicates a radio frame starting the repeated transmission of the PRACHsignal.
 9. The UE according to claim 8, wherein the processor monitorsthe downlink control information in a random access response (RAR)window, the RAR window indicating a time interval for detecting theRA-RNTI and receiving a random access response, and wherein theprocessor determines a start subframe of the RAR window by adding aspecific subframe offset to a subframe ending the repeated transmissionof the PRACH signal.
 10. The UE according to claim 9, wherein thespecific subframe offset is 3 subframes.
 11. The UE according to claim8, wherein a number of repetitions for transmitting the PRACH signal isdetermined based on a reference signal received power (RSRP)measurement.
 12. The UE according to claim 8, wherein the processorreceives system information comprising information about random accessresponse (RAR) window sizes, the RAR window sizes being independentlyconfigured for a plurality of PRACH resources configured for the UE, andwherein the processor determines a size of the RAR window as a RARwindow size configured for a PRACH resource used for transmitting thePRACH signal.
 13. The UE according to claim 8, wherein a time intervalfor the repeated transmission of the PRACH signal is extended over aplurality of radio frames.
 14. The UE according to claim 13, whereineach radio frame comprises 10 subframes.